Genes and Mutations in Hearing Impairment - Genetics of Auditory Disorders - page 30

FIGURE 2.6. Mutations may be in the form of deletions, insertions or substitutions.
In (A) and (B), a deletion or insertion of one nucleotide forms a frameshift, chang-
ing the subsequent amino acids. In (C), a transversion leads to a missense mutation,
affecting only one amino acid. In (D), a transition leads to a nonsense mutation,
forming a stop codon.

TABLE 2.2. Types of DNA mutations
DNA mutation Examples of resulting mutation

Point (substitution, transversion or transition) Missense—altered amino acid

Nonsense—stop codon

Deletion/ insertion
Multiple of 3 Deletion/insertion of amino acid(s)

Not a multiple of 3 Frameshift, truncation

variant and may occur naturally in the population, rather than be the cause
of a disease. Finally, when a DNA mutation changes the amino-acid codon
to a stop codon (UAA, UAG, or UGA in RNA), a nonsense mutation
occurs. This mutation can lead to protein truncation and can clearly affect
protein function.
Insertions and deletions of DNA nucleotides also change the encoded
protein. The addition or deletion of three nucleotides will add or delete an
amino acid, which may have dire consequences for the protein. Alterna-